However, Mr Balls said that if he became chancellor he would be ready to consider borrowing more money for major infrastructure building immediately.

Investment in roads, house-building and other projects would give the economy a boost and George Osborne should commit £10 billion to such schemes now, he said.

Asked on the BBC’s Andrew Marr show whether he would be ready to borrow more after the 2015 election, Mr Balls said: “Of course.

“The reason is, if the economy is still weakening, living standards are still falling, if youth unemployment’s still high, if there’s still a case on our long-term infrastructure to get things moving with interest rates low, of course there’s a case for doing that.

“It would be economically very foolish to deny that.”

He maintained that if Mr Osborne had borrowed more money to spend on such projects instead of cancelling capital spending plans “we wouldn’t have had such a flat-lining economy”.

Mr Balls added: “I’m not going to make the same mistake.”

Labour will keep the coalition’s Whitehall budget cuts of £11.5 billion for the 2015-16 financial year, which Mr Osborne is due to detail in next week’s spending review.

The party will inherit “a big deficit” if it wins the next election and “therefore we’ll be matching their plans”.

Mr Balls warned that Labour could not promise to protect state pensions from cuts in the longer term.

He confirmed that pension spending would be included in Labour’s plan to put a cap on welfare spending, but urged people to ignore “scare stories” from the Conservatives that Labour would cut the state pension.

“We’ve said we’re going to have a cap that needs to look across all of social security and welfare spending.

“We’ve said on the basic pension for the next few years, we’ll support the Government on the triple-lock which means pensions are being uprated.”

However, he added that there was “a debate to be had” about whether or not the country has achieved “long-term affordability in pensions”.

“I don’t think it’s possible to have a debate about affordability in our social system and welfare state in the next 50 years and ignore the part of spending, which is more than half of spending, which goes to people over 60.

“It means that people of my generation or the younger generations are going to work longer than our parents and grandparents – that’s all about basic pension spending and affordability.”

He added: “In the short term, ignore the Tory scares – we will make sure that pension rises are properly protected.”

Sajid Javid, the Conservative Economic Secretary to the Treasury, said that Mr Balls had undermined Mr Miliband’s promise to show “discipline” with taxpayers’ money.

“Ed Miliband's spending 'discipline' has barely lasted five minutes as Ed Balls admits Labour would still spend more and borrow more. That's the same old Labour approach that got us into this mess in the first place,” he said.

“Hardworking people would pay the price with higher interest rates and higher bills.”